OOP 원칙은 PDO를 사용하여 PHP에서 데이터베이스 연결 처리를 어떻게 향상시킬 수 있습니까?

class Database {
    private $conn;
    private $dsn = 'mysql:dbname=test;host=127.0.0.1';
    private $user = 'root';
    private $password = '';

    public function __construct() {
        $this->conn = new PDO($this->dsn, $this->user, $this->password);
        return $this->conn;
    }
}

include "database.php";

class User {
    private $conn;

    public function __construct() {
        $this->conn = new Database();
    }

    public function login() {
        $stmt = $this->conn->prepare("SELECT username, usermail FROM user");
        // Rest of the code...
    }
}

$user = new User();
$list = $user->login();
// Rest of the code...

// Define database connection parameters
$host = '127.0.0.1';
$db   = 'test';
$user = 'root';
$pass = '';
$charset = 'utf8';

// Create a PDO connection
$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$opt = [
    \PDO::ATTR_ERRMODE            => \PDO::ERRMODE_EXCEPTION,
    \PDO::ATTR_DEFAULT_FETCH_MODE => \PDO::FETCH_ASSOC,
    \PDO::ATTR_EMULATE_PREPARES   => false,
];
$pdo = new \PDO($dsn, $user, $pass, $opt);

class User {
    private $conn;

    public function __construct(\PDO $pdo) {
        $this->conn = $pdo;
    }

    public function getUsers() {
        return $this->conn->query("SELECT username, usermail FROM user")->fetchAll();
    }
}

include 'database.php';
$user = new User($pdo);
$list = $user->getUsers();
// Rest of the code...